G'day Rolf,

That feature was introduced in v5.34: "perl5340delta: Blanks freely allowed within but adjacent to curly braces".

My tests:

$ alias perle
alias perle='perl -Mstrict -Mwarnings -Mautodie=:all -MCarp::Always -E
+'

$ perlbrew switch perl-5.32.0

$ perle 'say $]; say join ",",map {ord} split //, $_ for "\x{ 41 }", "
+\x{41}", "\x{263A}", "\x{ 263A }"; say for "\x{41}", "\x{ 41 }"'
Non-hex character ' ' terminates \x early.  Resolved as "\x{00}" at -e
+ line 1.
Non-hex character ' ' terminates \x early.  Resolved as "\x{00}" at -e
+ line 1.
Non-hex character ' ' terminates \x early.  Resolved as "\x{00}" at -e
+ line 1.
5.032000
0
65
9786
0
A


$ perlbrew switch perl-5.34.0

$ perle 'say $]; say join ",",map {ord} split //, $_ for "\x{ 41 }", "
+\x{41}", "\x{263A}", "\x{ 263A }"; say for "\x{41}", "\x{ 41 }"'
5.034000
65
65
9786
9786
A
A
[download]

It's not mentioned in perlop, so a doco omission but not a bug in Perl itself. Perhaps raise a doco bug report.